Glass-like polymeric antireflective films coated with silica nanoparticles, methods of making and light absorbing devices using same

Abstract

A transparent anti-reflective structured film comprising a structured film substrate having a structured face, with anti-reflective structures defining a structured surface. The structured face is anti-reflective to light, with at least a substantial portion of the structured surface comprising a glass-like surface. At least the anti-reflective structures comprise a cross-linked silicone elastomeric material, and the glass-like surface comprises an SiO 2 stoichiometry. The glass-like surface is coated with a coating of at least one layer of agglomerates of silica nanoparticles, with the agglomerates comprising a three-dimensional porous network of silica nanoparticles, and the silica nanoparticles being bonded to adjacent silica nanoparticles. A light energy absorbing device comprising the transparent anti-reflective structured film disposed so as to be between a source of light energy and a light energy receiving face of a light absorber, when light energy is being absorbed by the light absorber.

1 . A transparent anti-reflective structured film comprising:
 a structured film substrate having a structured face, with said structured face comprising anti-reflective structures defining a structured surface and being anti-reflective to light, at least a substantial portion of said structured surface comprising a glass-like surface, at least said anti-reflective structures comprising a cross-linked silicone elastomeric material, and said glass-like surface comprising an SiO 2  stoichiometry and being coated with a coating of at least one layer of agglomerates of silica nanoparticles, with said agglomerates comprising a three-dimensional porous network of silica nanoparticles, and the silica nanoparticles being bonded to adjacent silica nanoparticles.   
     
     
         2 . The film according to  claim 1 , wherein said glass-like surface comprises said SiO 2  stoichiometry to a depth of at least about 5 nanometers into each of said anti-reflective structures. 
     
     
         3 . The film according to  claim 1 , wherein said glass-like surface comprises said SiO 2  stoichiometry to a depth in the range of from at least about 10 nanometers to about 100 nanometers into each of said anti-reflective structures. 
     
     
         4 . The film according to  claim 1 , wherein said glass-like surface comprises a minimum amount of at least about 10 molar % carbon atoms. 
     
     
         5 . The film according to  claim 1 , wherein said glass-like surface comprises in the range of from a minimum amount of at least about 10 molar % carbon atoms up to about 40 molar % carbon atoms. 
     
     
         6 . The film according to  claim 1 , wherein said anti-reflective structures comprise prisms having a prism tip angle in the range of from about 15 degrees to about 75 degrees and a pitch in the range of from about 10 microns to about 250 microns. 
     
     
         7 . The film according to  claim 1 , wherein said anti-reflective structures comprise prisms having a trough to peak height in the range of from about 10 microns to about 250 microns. 
     
     
         8 . The film according to  claim 1 , wherein said film exhibits a change in light transmission of less than 8%, after said structured surface is exposed to at least one of the Dirt Pick-Up Test and the Falling Sand Test. 
     
     
         9 . A light energy absorbing device comprising:
 a light absorber having a light energy receiving face; and   a transparent anti-reflective structured film, according to  claim 1 , disposed so as to be between a source of light energy and said light energy receiving face, while light energy from the source is being absorbed by said light absorber.   
     
     
         10 . A method of making a transparent anti-reflective structured film, said method comprising:
 providing a structured film substrate having a structured face comprising anti-reflective structures defining an anti-reflective structured surface that is anti-reflective to light, with at least the anti-reflective structures comprising a cross-linked silicone elastomeric material; and   treating the anti-reflective structured surface so as to transform cross-linked silicone elastomeric material defining at least a substantial portion of the anti-reflective structured surface into a glass-like material comprising an SiO 2  stoichiometry, such that at least a substantial portion of the anti-reflective structured surface comprises a glass-like surface having the SiO 2  stoichiometry; and   coating the glass-like surface with a coating of at least one layer of agglomerates of silica nanoparticles, with said agglomerates comprising a three-dimensional porous network of silica nanoparticles, and the silica nanoparticles being bonded to adjacent silica nanoparticles.   
     
     
         11 . The film according to  claim 1 , wherein the anti-reflective structures comprise prisms having a prism tip angle of less than about 90 degrees, less than or equal to about 60 degrees, or in the range of from about 10 degrees up to about 90 degrees and a pitch in the range of from about 2 microns to about 2 cm. 
     
     
         12 . The film according to  claim 1 , wherein the film exhibits at least about 80% light transmission, after the structured surface is exposed to the Dirt Pick-Up Test, the Falling Sand Test, or both tests. 
     
     
         13 . The film according to  claim 1 , wherein the structured surface exhibits a storage modulus of at least about 20 MPa, and the remainder of each anti-reflective structure exhibits a lower storage modulus than that exhibited by the structured surface. 
     
     
         14 . The film according to  claim 1 , further comprising inorganic in the cross-linked silicone elastomeric material of at least the anti-reflective structures. 
     
     
         15 . The film according to  claim 1 , in combination with a barrier layer, wherein the structured film substrate further comprises a backing face, and the barrier layer is bonded to the backing face of the structured film substrate. 
     
     
         16 . The film according to  claim 15 , wherein the barrier layer is a moisture barrier. 
     
     
         17 . The film according to  claim 1 , wherein the coating comprises:
 a) from about 60 wt. % to about 95 wt. % of the agglomerates of silica nanoparticles;   b) from about 0.1 wt. % to about 20 wt. % of at least one or more tetraalkoxysilanes;   c) optionally from about 0 wt. % to about 5 wt. % of a surfactant; and   d) optionally from about 0 wt. % to about 5 wt. % of a wetting agent.   
     
     
         18 . The film according to  claim 1 , wherein the coating comprises:
 a) from about 0.5wt. % to about 99 wt. % water;   b) from about 0.1 wt. % to about 20 wt. % of the silica nanoparticles having an average particle diameter of 40 nm or less;   c) optionally from about 0 wt. % to about 20 wt. % of the silica nanoparticles having an average particle diameter of greater than about 50 nm, wherein the sum of b) and c) is from about 0.1 wt. % to about 20 wt. %;   d) a sufficient amount of an acid having a pKa of <3.5 to reduce the pH to less than 5; and   e) optionally from about 0 wt% to about 20 wt. % of a tetraalkoxysilane, relative to the amount of the silica nanoparticles.